Merge the list in the README to render better on GitHub

Author: eregon

README.md

@@ -96,8 +96,6 @@ jobs:
 * short version like `2.6`, automatically using the latest release matching that version (`2.6.5`)
 * version only like `2.6.5`, assumes MRI for the engine
 * engine only like `truffleruby`, uses the latest stable release of that implementation
-
-
 * `.ruby-version` reads from the project's `.ruby-version` file
 * `.tool-versions` reads from the project's `.tool-versions` file
 * If the `ruby-version` input is not specified, `.ruby-version` is tried first, followed by `.tool-versions`